1. Field of the Invention
The present invention relates to a method of forming bumps and a bonding tool for forming bumps, a semiconductor wafer, a semiconductor chip and a semiconductor device, and methods of fabrication thereof, a circuit board and an electronic instrument.
2. Description of the Related Art
Methods of forming a bump on an electrode of a semiconductor chip using wire bonding technology are well known. For example, Japanese Patent Application Laid-Open No. 57-163919 discloses a method in which a wire is bonded to an electrode by a capillary, and the wire is then torn off so that a fragment of the wire remains on the electrode to form a bump. This method is able to form a bump more rapidly than by cumulative plating.
However, a bump formed by tearing off a wire does not adequately assure a flat upper surface, and therefore while no problems occur when using face-down bonding of a semiconductor chip on a substrate, when bonding a lead to a bump there is a problem of inferior junction accuracy. That is to say, since an upper surface of the bump is jagged or has very little surface area that is flat, the bonding area with the lead is insufficient, and the lead tends to slip off the bump.
The present invention solves this problem, and has as its objective the provision of a method of forming a bump and a bonding tool for forming a bump, a semiconductor wafer, a semiconductor chip and a semiconductor device, and methods of fabrication thereof, a circuit board and an electronic instrument such that a bump having a large bonding area can be formed easily.
(1) According to a first aspect of the present invention, there is provided a method of forming a bump, comprising: a first step of bonding a ball-shaped tip portion of a conductive wire to an electrode by a first tool so that a portion of the tip portion, positioned around a central portion that leads to the conductive wire and avoiding an outer peripheral portion, is pressed and plastically deformed by the first tool; a second step of tearing off the conductive wire in such a manner that the tip portion remains on the electrode; and a third step of pressing at least the central portion of the tip portion by a second tool to cause plastic deformation.
The ball-shaped tip portion of the conductive wire is bonded to the electrode, and a part of the tip portion is pressed and plastically deformed. The part to be pressed and plastically deformed is a portion around the central portion of the ball-shaped tip portion except the outer peripheral portion. As a result, there is a groove around the central portion of the tip portion after plastic deformation, and the outer peripheral portion remains undeformed. The conductive wire is then torn off in such a manner that the tip portion including the plastically deformed part remains on the electrode, and then at least the central portion of the tip portion is pressed and plastically deformed. As a result, the central portion of the tip portion is commonly made flat. With the bump formed in this way, since the outer peripheral portion of the ball-shaped tip portion is not deformed in the first step, the upper surface of the outer peripheral portion can also be used as a bonding area. Thus, according to the present invention, a bump having a large bonding area can be formed easily.
(2) According to a second aspect of the present invention, there is provided a method of forming a semiconductor wafer, comprising: a first step of forming an integrated circuit and a plurality of electrodes, and then bonding a ball-shaped tip portion of a conductive wire to one of the electrodes by a first tool so that a portion of the tip portion, positioned around a central portion that leads to the conductive wire and avoiding an outer peripheral portion, is pressed and plastically deformed by the first tool; a second step of tearing off the conductive wire in such a manner that the tip portion remains on the one of the electrodes; and a third step of pressing at least the central portion of the tip portion by a second tool to cause plastic deformation.
The ball-shaped tip portion of the conductive wire is bonded to the electrode, and a part of the tip portion is pressed and plastically deformed. The part to be pressed and plastically deformed is a portion around the central portion of the ball-shaped tip portion except the outer peripheral portion. As a result, there is a groove around the central portion of the tip portion after plastic deformation, and the outer peripheral portion remains undeformed. The conductive wire is then torn off in such a manner that the tip portion including the plastically deformed part remains on the electrode, and then at least the central portion of the tip portion is pressed and plastically deformed. As a result, the central portion of the tip portion is commonly made flat. With the bump formed in this way, since the outer peripheral portion of the ball-shaped tip portion is not deformed in the first step, the upper surface of the outer peripheral portion can also be used as a bonding area. Thus, according to the present invention, a semiconductor wafer which has a bump having a large bonding area can be formed easily.
(3) In this method of forming a semiconductor wafer, the first and second steps may be repeated before the third step in such a manner that the tip portion of the conductive wire remains on each of the electrodes; and a plurality of bumps may be simultaneously formed by pressing a plurality of tip portions remaining on the electrodes simultaneously in the third step.
As described, since a plurality of bumps can be formed simultaneously, the process time can be reduced.
(4) According to a third aspect of the present invention, there is provided a method of forming a semiconductor chip, comprising: a first step of cutting a semiconductor wafer having an integrated circuit and a plurality of electrodes into pieces each having a group of electrodes from the plurality of electrodes, and then bonding a ball-shaped tip portion of a conductive wire to one electrode in the group of electrodes by a first tool so that a portion of the tip portion, positioned around a central portion that leads to the conductive wire and avoiding an outer peripheral portion, is pressed and plastically deformed by the first tool; a second step of tearing off the conductive wire in such a manner that the tip portion remains on the one of the electrodes; and a third step of forming a bump by pressing at least the central portion of the tip portion by a second tool to cause plastic deformation.
The ball-shaped tip portion of the conductive wire is bonded to the electrode, and a part of the tip portion is pressed and plastically deformed. The part to be pressed and plastically deformed is a portion around the central portion of the ball-shaped tip portion except the outer peripheral portion. As a result, there is a groove around the central portion of the tip portion after plastic deformation, and the outer peripheral portion remains undeformed. The conductive wire is then torn off in such a manner that the tip portion including the plastically deformed part remains on the electrode, and then at least the central portion of the tip portion is pressed and plastically deformed. As a result, the central portion of the tip portion is commonly made flat. With the bump formed in this way, since the outer peripheral portion of the ball-shaped tip portion is not deformed in the first step, the upper surface of the outer peripheral portion can also be used as a bonding area. Thus, according to the present invention, a semiconductor chip which has a bump having a large bonding area can be formed easily.
(5) In this method of forming a semiconductor chip, wherein the first and second steps may be repeated before the third step in such a manner that the tip portion of the conductive wire remains on each electrode in the group of electrodes; and a plurality of bumps may be simultaneously formed on the group of electrodes by pressing a plurality of tip portions remaining on the group of electrodes simultaneously in the third step.
Since a plurality of bumps can be formed simultaneously, the process time can be reduced.
(6) According to a fourth aspect of the present invention, there is provided a method of forming a semiconductor device comprising: a first step of bonding a ball-shaped tip portion of a conductive wire to one of a plurality of electrodes of a semiconductor chip by a first tool so that a portion of the tip portion, positioned around a central portion that leads to the conductive wire and avoiding an outer peripheral portion, is pressed and plastically deformed by the first tool; a second step of tearing off the conductive wire in such a manner that the tip portion remains on the one of the electrodes; a third step of forming a bump by pressing at least the central portion of the tip portion by a second tool to cause plastic deformation; and a fourth step of bonding the bump to a lead.
The ball-shaped tip portion of the conductive wire is bonded to the electrode, and a part of the tip portion is pressed and plastically deformed. The part to be pressed and plastically deformed is a portion around the central portion of the ball-shaped tip portion except the outer peripheral portion. As a result, there is a groove around the central portion of the tip portion after plastic deformation, and the outer peripheral portion remains undeformed. The conductive wire is then torn off in such a manner that the tip portion including the plastically deformed part remains on the electrode, and then at least the central portion of the tip portion is pressed and plastically deformed. As a result, the central portion of the tip portion is commonly made flat. With the bump formed in this way, since the outer peripheral portion of the ball-shaped tip portion is not deformed in the first step, the upper surface of the outer peripheral portion can also be used as a bonding area. In this manner, a bump having a large bonding area can be formed easily. Then by bonding a lead to this bump, a semiconductor device can be obtained.
(7) In this method of forming a semiconductor device, wherein the first and second steps may be repeated before the third step in such a manner that the tip portion of the conductive wire remains on each of the electrodes; and a plurality of bumps may be simultaneously formed on the electrodes by pressing a plurality of tip portions remaining on the electrodes simultaneously in the third step.
As described, since a plurality of bumps can be formed simultaneously, the process time can be reduced.
(8) In this method of forming a semiconductor device, the lead may protrude into an opening formed in a substrate; and the bump may be disposed within the opening such that the lead is bonded to the bump within the opening in the fourth step.
(9) In this method of forming a semiconductor device, the lead may be formed on a substrate; and the bump may be arranged to face the lead on the substrate for the face-down bonding of No the semiconductor chip in the fourth step.
(10) In this method of forming a semiconductor device, the bump may be bonded to the lead by means of an anisotropic conductive material formed of conductive particles dispersed within an adhesive in the fourth step.
(11) According to a fifth aspect of the present invention, there is provided a bonding tool for forming a bump, wherein an aperture for passing a conductive wire which has a ball shaped tip portion is formed; wherein a pressing portion is provided around the aperture for pressing the tip portion of the conductive wire; and wherein the pressing portion has a shape that enables pressure to be applied to the tip portion avoiding an outer peripheral portion of the tip portion.
The ball-shaped tip portion of the conductive wire is passed through the aperture, and a part of the tip portion is pressed by the pressing portion. The part to be pressed is a portion around the central portion of the ball-shaped tip portion except the outer peripheral portion. Therefore, plastic deformation can be performed avoiding the outer peripheral portion of the tip portion. The conductive wire is then torn off in such a manner that the tip portion including the plastically deformed part remains on the electrode, and then at least the central portion of the tip portion is pressed and plastically deformed. By pressing the central portion of the tip portion, a bump in which an upper surface of the outer peripheral portion can also be used as a bonding area is formed. Thus, according to the present invention, a bump having a large bonding area can be formed easily.
(12) According to a sixth aspect of the present invention, there is provided a semiconductor wafer comprising an integrated circuit, a plurality of electrodes, and a bump formed on each of the electrodes, wherein a groove is formed between a central portion and an outer peripheral portion on a top surface of the bump, the heights of the central portion and the outer peripheral portion being substantially equal.
Since the outer peripheral portion that is formed outside the groove on the periphery of the central portion of the bump is at substantially the same height as the central portion, the entire upper surface of the bump forms a bonding area, and a large bonding area is available.
(13) According to a seventh aspect of the present invention, there is provided a semiconductor chip comprising an integrated circuit, a plurality of electrodes, and a bump formed on each of the electrodes, wherein a groove is formed between a central portion and an outer peripheral portion on a top surface of the bump, the heights of the central portion and the outer peripheral portion being substantially equal.
Since the outer peripheral portion that is formed outside the groove on the periphery of the central portion of the bump is at substantially the same height as the central portion, the entire upper surface of the bump forms a bonding area, and a large bonding area is available.
(14) According to an eighth aspect of the present invention, there is provided a semiconductor device, comprising: a semiconductor chip having a plurality of electrodes; a bump formed on each of the electrodes, in which a groove is formed between a central portion and an outer peripheral portion on a top surface, the heights of the central portion and the outer peripheral portion being substantially equal; a lead bonded to the bump; and a substrate on which the lead is formed.
Since the outer peripheral portion that is formed outside the groove on the periphery of the central portion of the bump is at substantially the same height as the central portion, the entire upper surface of the bump forms a bonding area, and a large bonding area is available, as a result of which a good connection with the lead is possible.
(15) In this semiconductor device, the substrate may have an opening; the lead may protrude into the opening in the substrate; and the bump may be bonded to the lead within the opening.
(16) In this semiconductor device, the lead may be formed on the substrate; and the bump may be arranged to face the lead on the substrate for the face-down bonding of the semiconductor chip.
(17) In this semiconductor device, the bump may be bonded to the lead by an anisotropic conductive material formed of conductive particles dispersed within an adhesive.
(18) According to a ninth aspect of the present invention, there is provided a circuit board on which the semiconductor device as described is mounted.
(19) According to a tenth aspect of the present invention, there is provided an electronic instrument comprising the semiconductor device as described.